A photovoltaic (PV) array is a linked collection of solar panels (modules), which are made of multiple interconnected solar cells that convert light energy into direct electrical current (DC), via the photovoltaic effect. However, most commercial and residential applications of electricity require alternating electrical current (AC) that typically is provided by power generating facilities utilizing coal, nuclear material, or water. Upon generating the alternating current, the power generating facilities transmit the generated alternating current into an electrical grid system.
In order for most commercial and residential users to utilize the electricity generated by the solar panels, the direct current from the solar panels is typically transformed into alternating current. This is achieved by way of an electrical device known as an inverter, the output of which is subsequently tied to the electrical grid system. In turn, the alternating current is distributed via the electrical grid system to commercial and residential sites.
Currently, in the United States, a conventional solar panel string (for example, consisting of cadmium telluride (CdTe) or amorphous silicon) comprises six solar panels which are wired in series, where each such solar panel string inherently operates at a voltage of approximately 372 VDC with an operating current of 0.87 amps. A set of the series solar panel strings is then wired in parallel to form a row, where a set of the rows form the solar array that produces a desired total current.
In general, regarding electrical safety for the general public, exposure to the public is regulated by the National Electrical Code (NEC), where people are not to come in contact with voltages over 42 volts (V) (and facilities are not to have a voltage above 600 V. Hence, many components (e.g., wire, fuses, and switches) are rated for operation up to and including the 600 V limit.
On the other hand, the National Electrical Safety Code (NESC) regulates electrical generating and distributing facilities, wherein skilled workers in such facilities may be exposed to high voltages that can exceed 600 volts.
Although much work has been done to generate direct current by way of solar panels and then to invert the direct current to alternating current for tie-in to the electrical grid, the solar industry has been hindered by overall low power efficiency rates associated with converting sunlight energy into useable alternating current by inverters.
It would be desirable to develop a grid tie system for tying a solar array to an electrical grid and a method of controlling the grid tie system, wherein the system and method maximize a harvesting of energy under low light level conditions and a reliability of the system through selective activation of an inverter of the system.